1. Field of the Invention
The present invention relates to the field of flat panel displays, and in particular to a thin-film transistor array substrate and a manufacturing method thereof.
2. The Related Arts
Active matrix flat panel displays have various advantages, including thin device body, low power consumption, and being free of radiations, and have been widely used. The flat panel displays that are currently available in the market include liquid crystal displays (LCDs) and organic light-emitting diode (OLED) displays.
An LCD comprises a liquid crystal display panel and a backlight module. The principle of operation of the liquid crystal display panel is that with liquid crystal molecules interposed between two parallel glass substrates, electricity is applied to the glass substrates to control if the direction of the liquid crystal molecules is changed so as to refract out light from the backlight module to generate an image.
An OLED has characteristics including being self-luminous, high brightness, wide view angle, high contrast, being flexible, and lower power consumption and has attracted wide attention as being a new generation displaying measure that has gradually taken the place of the traditional LCDs and has been widely used in mobile phone screens, computer monitors, and full-color televisions. The OLED display technology is different from the traditional liquid crystal display technology and requires no backlighting and involves extremely thin organic material coating layer and glass substrate, wherein when electricity is conducted to flow therethrough, the organic material gets luminous.
Thin-film transistor array substrates have been widely used in LCDs and OLEDs and generally comprise a glass base plate and thin-film transistors and storage capacitors formed on the glass base plate.
The storage capacitors play an important role of maintaining electrical potential and reducing divided voltage of coupling capacitors. Generally speaking, it is desired to have a relatively large capacitance. Capacitance is calculated according to the formula: C=∈S/D, where S is surface area and D is thickness of insulation. To change the capacitance of a storage capacitor, several ways may be taken; (1) using an insulation material having a large dielectric constant; (2) increasing the surface area; and (3) reducing the thickness of the insulation material.
Generally speaking, expanding the areas of opposite surfaces of two metal plates would increase capacitance. However, since a storage capacitor is made up of an insulation layer interposed between metals and the metal electrodes are generally not light transmittable, the larger the storage capacitor is, the smaller the aperture ratio would be. Reducing the thickness of the insulation layer can increase the storage capacitance and may also, on the same basis, allows for reduction of the areas of the opposite surfaces of the metal plates, and is thus considered a better way of increasing the storage capacitance and simultaneously increasing the aperture ratio.
Referring to FIG. 1, a cross-sectional view is given to illustrate the structure of a conventional thin-film transistor array substrate, which comprises a base plate 100 and a thin-film transistor and a storage capacitor formed on the base plate 100. The storage capacitor comprises a first electrode plate 310 and a second electrode plate 320 between which a gate insulation layer 300 and an etch stop layer 500 are interposed. Since the gate insulation layer 300 and the etch stop layer 500 each have a certain thickness, the insulation layer, as a whole, is thus relatively thick, requiring a relatively large area of opposite surfaces to provide a desired capacitance thereby making the aperture ratio of the device lowered.